text:
Power assisted flying control unit

What is the working principle and operation sequence of the power assisted flying control unit?

Please specify what is not already obvious!

It's just the same as power-assisted steering in a motor vehicle or marine vessel.  What did you think might be different?

This hydraulic device is a general design used in many mechanical systems. It relies on two principles:

hydraulic jack
positive feedback loop.

It you prefer video to written explanations, just watch this.
The top section is a valve (a sliding spool four-way directional control valve) injecting pressurized red fluid either on the left or on the right side of the bottom section piston depending on the stick position (it wouldn't work as shown, the pivot between the stick and the valve prevents any translation of the top rod, this pivot must be removed).
The red pressurized fluid entering the bottom cylinder moves the piston, the elevator (or aileron) moves and a positive feedback force is also applied to the stick by the bottom rod, allowing to initiate the displacement with a very small force and let the piston provide the additional force necessary for the action to complete.
As in any jack or hydraulic press, a small input force is converted into a larger one. The gain in magnitude is proportional to the ratio of the areas of the fluid inlet and the piston, explained here.
As the red fluid enters the cylinder on one side of the piston, it must be drained on the other side. Draining is done by connecting the cylinder to the yellow circuit, the control valve is designed to allow these two connections while preventing the red and yellow circuits to be interconnected. Of course the pressure in the yellow circuit must be lower than in the red circuit. The yellow circuit returns the fluid to the tank, it is pressurized again and pumped back into the red circuit.

Good answer.  The diagram may work if the housing moves and the piston is stationary.  (Housing movement is the output).


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“X” letter meaning next to VHF frequency in jeppessen plates
DOH airport implemented new VHF frequencies in their new SID/STAR/APP jeppessen charts.
What does the « X »letter means next to these frequencies

source: Stack Exchange

license: Creative Commons - Attribution Share-Alike - https://creativecommons.org/licenses/by-sa/4.0/

sort: votes


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How can I choose an airfoil for inverted flight & high weight payload?
I have a project for university to design and build a model RC aircraft. Tt's main design principal is to carry a high payload, so I was thinking of going for a high camber, thick aerofoil. Hopefully this will allow it to carry a heavy weight at low speeds.
However, one of the other requirements is that it must be able to fly inverted for 4s without load.
How should this impact my choice of aerofoil, is at all? And what are some suggested types of aerofoil I should look at for these requirements?

I’m voting to close this question because questions about RC aircraft belong on Drones.SE.

Even though the scenario is unlikely for full-size aircraft, the reasoning would be exactly the same, so I don't see why it should be closed.

First a couple of suggestions.  When you are talking about "high weight payload" this is completely arbitrary.  Instead try to think about it in terms of weight fraction of design gross weight or similar parameter.  This puts the problem into perspective.  a 10 lbs payload for a 15 lb aircraft is a big deal.  Also low airspeeds equates to what? 30 kts? 15 kts?  Giving more specifics on design criteria will help you get a better answer.

How big in meters (or cm) should it be? MTOW? Configuration (conventional, canard, payload in cargo bay or underwing, swept wing, delta wing, flying wing)? Max speed, stall speed, ...

@Raketenolli  The Reynolds number would be fairly different for an RC vs a full-size aircraft, and that drives some differences. Picture the wings of a simple paper airplane... that shape works fine for fold-it-and-throw-it, but not so well for larger, heavier, and faster.  Since the assignment here is literally a drone, this would fit better at Drones.SE.

What do you mean fly inverted for 4s without load? That is called falling while inverted.

In general to start a preliminary aircraft design problem you need to start with basic parameters such as configuration and geometric parameters which will contribute to GTOW, available power, target stall speed etc.  Intro to Flight by John D Anderson is a great starting point for basic design parameters.  In particular look at chapters 5,6 & 7.
If you know your target stall speed and guess at your max weight you can determine the lift coefficient you will need.  This will be a starting point for evaluating airfoils.  Airfoil Tools is a great resource for searching sorting and gathering data.  You'll also want to look at performance at a target cruise/loiter speed.  You can approach it from different directions, also depending on control surfaces.  Yet another factor is flight performance.  How long does it need to fly for?  10 minutes carrying a heavy payload is pretty easy compared to 3 hours.
These are all things you need to consider.  Saying a thick high camber airfoil is a generic starting point and maybe totally unnecessary.  Think about the Piper J-3 that uses the tried and true Clark Y but achieves a really low stall speed.  You really need to factor in the whole vehicle to get a "good" design.

However, one of the other requirements is that it must be able to fly inverted for 4s without load.

How should this impact my choice of aerofoil, is at all?

I'm going to assume that "without load" means "without payload", not "in a zero-G condition".
I'm going to also assume that there is no requirement that the altitude be constant during the inverted segment-- i.e. I'm going to assume that descending flight is allowed.
If so, the 4-second inverted requirement should have no effect on your airfoil choice.
As a strategy to intentionally lose altitude, I've held a "E-flite Radian" radio-controlled motor glider in unpowered (descending) inverted flight for literally minutes on end.  The Radian has an undercambered airfoil that is far from optimal for efficient inverted flight. Yet the resulting best glide angle in unpowered, inverted flight is still relatively flat (perhaps 10 to 20 degrees below horizontal?)
Your primary issues in a brief segment of inverted flight will revolve around structural integrity and controllability (especially if the wing has dihedral, which degrades controllability in inverted flight), not airfoil efficiency.
(Hint: don't assume that the requirement to demonstrate inverted flight rules-out a no-aileron design, with ample dihedral, and with rudder and elevator as the only control surfaces.  Such designs can in fact be flown inverted for prolonged periods by a proficient pilot, so long as the rudder is sufficiently large and has ample throw.
The "Radian" glider mentioned above, when set up optimally, is an example of such a design.)
In fact my recommendation would be the same even if the requirement were that the aircraft must maintain altitude while inverted, with zero payload.  Back to the "Radian" motorglider as example-- despite the undercambered airfoil, it is perfectly capable of a modest sustained climb rate in inverted, powered flight.  So design the airfoil for efficient sustained upright flight with the required payload, not for the brief no-payload inverted segment.
Another note-- depending on the exact rules at play, and the discretion of the judges, you might consider doing the inverted section as part of loop.  Would the judges count all portions of the loop where the aircraft was even slightly inverted, as contributing to the required 4 seconds?  If so, depending on entry speed (the higher the better), it seems quite possible that you could meet the 4-second-inverted requirement with the G-loading (and therefore the lift force) never even going negative at all, or only going slightly negative for a brief interval.
Another way to show how much you can "get away with", for brief intervals of time, in terms of non-optimal airfoil choices, is to take a radio-controlled model airplane with flaps and experiment with sustained inverted flight with the flaps down.  You might be surprised at what is possible!  Design your airfoil for the main mission, not for the 4 seconds of inverted flight.

So thorough!  The only point you might add is, while flying inverted, to put the flaps "up" to restore the desired camber.

@CamilleGoudeseune - actually I was thinking of flaps "down" from airplane's point of view, just as a demonstration, to make the airfoil really non-optimal!

Yes, you were clear:  if a shape that terrible still works, there's zero justification for compromising the main task's performance.  I only noted that, hey, while we're talking flaps, reversing them is a cheap way to improve performance while inverted.

I read the initial statement "without load" as specifically not in a loop where there will be G loading, but rather as steady-state inverted flight.  Are you trying to suggest that it also has to fly with no payload for a separate flight or that it somehow has to dump its payload to fly inverted?

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New airplane certification required for airplanes operated by non-American airlines?
I read the news today that Chinese made C919 is certified by its government.   Does FAA need to certify this aircraft before it can land in the US even thought operated by a Chinese airline ( or any other non-American airlines)?

C919 isn't a plane that's supposed to fly a trans-pacific route.....

@user3528438 That was my first reaction to the question. Why would a Chinese aircraft manufacturer seek FAA certification for an aircraft that is meant to operate almost entirely in the domestic and/or Asia markets, will likely not find buyers in the US, and doesn't have the range to fly to any US airports in the first place unless it's a non-pax ferry flight with special interior tanks?

The Chicago Convention states that aircraft certification is up to the state of registration, regardless of which state it’s operating in.
So, if the Chinese govt certifies an aircraft registered in China as airworthy, then it can legally operate in any member state.  In theory, the FAA wouldn’t even be involved until someone wanted to register that aircraft in the US.
However, in practice the leading aviation regulators (FAA, EASA, etc.) work together and have harmonized their requirements, so if an aircraft is certified in one of them, it can easily be certified in all the others. This also has the (probably intentional) side effect of nearly all aircraft design and production taking place in these countries, so China’s CAAC joining that club in 2017 was a big deal for them.

From what I read, Boeing 737 MAX needed to be recertified in both the US and China.

@ManyMore In the US for US-registered planes, in China for China-registered planes. Plus the MAX incident was not a normal case.

The Federal Aviation Administration (FAA) and the Civil Aviation Administration of China (CAAC) signed an implementing agreement in October of 2017 under the U.S. – China Bilateral Aviation Safety Agreement (BASA) recognizing each other’s regulatory systems with respect to the airworthiness of aviation products and articles.
FAA Press Release


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Why does bank angle have no effect on pivotal altitude?
Pivotal altitude is the height for a given ground speed at which the line of sight from the cockpit directly parallel to the lateral axis of the aircraft will remain stationary on an object on the ground.
It is also known that bank angle does not change pivotal altitude.
However, increasing bank angle tightens the radius of the turn for a given airspeed, as shown below, so why doesn't bank angle change the pivotal altitude?

The math just works out that way.

Assume zero wind. The airspeed $V$, turn radius $R$, gravitational acceleration $g$ and bank angle $\theta$ obey the relation $\frac{V^2}{R} = g\tan\theta$. Meanwhile, at the pivotal altitude $H$, the turn radius, altitude and bank angle obey $\frac{H}{R}=\tan\theta$.
Put the two together and you get that the altitude is $H=\frac{V^2}{g}$. At 50 meter/sec (just under 100 nm/h), this gives $H\approx250$ meters, or about 800'.
At a steeper bank angle you'll fly a tighter turn radius, and also need a tighter turn radius to put the wing on the center of the circle. Those two effects exactly match at the pivotal altitude.


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Is there a clear cut method for cutout on structural members?
I have been looking into fuselage cutouts especially, window cutouts on the skin panel for a school project. Reading Bruhn and Niu Books, both state that there are no clear cut methods for fuselage cutout yet before elaborating on methods based on empirical data. Is it due to the complexity that there is still no equation that may govern the shear flow direction and distribution around the cutout. Just a philosophical question I suppose, is there any other reason that may be a hindrance to from developing equation that is the "clear cut" method for cutouts. What are the mathematical/numerical methods used in this supercomputer era to properly simulate this situation?

I will assume the use of metal skins here.
Window cutouts can be made by machining with a rotating tool, cutting with a saw blade, shearing with powered scissors, punching in a powered die-cutting press, or chem-milling by applying a protective paint to the sheet metal everywhere you do not want a hole or cutout and then dipping it in acid to eat away the exposed holes.
The tooling required to perform these tasks varies greatly and so the method chosen will depend on the number of parts you intend to make, across which the tooling setup costs can be amortized. For a one-off plane like a homebuilt, you'll use shears or a saw and guide the process by hand. Mass production justifies punching, machining or chem-milling.
The method used will determine things like the fatigue lifetime of the resulting part. Shearing leaves microscopic stress risers in the form of microcracks at the end of each "snip" in the cutout profile whereas chem-milling leaves the cutout atomistically smooth all the way around.
Fuselage cutouts in the first revision of the De Havilland Comet were sheared and the resulting stress raisers caused premature fatigue failure of the pressure hull, which is why Boeing developed the chem-milling process to make the rivet holes and window cutouts in the 707.

The reason there's no straightforward equation for fuselage cutouts is because it's a really complicated problem. Fuselage structures are complex, and when you cut a hole in them, figuring out how the stress and forces are distributed is tough. It depends on the shape of the hole, the materials used, and how the airplane is loaded. Engineers use a mix of real-world testing, computer simulations, and their experience to design planes with cutouts. It's not that we don't understand it; it's just a really tricky puzzle to solve.

A lot of the books analyze the distribution of shear flow stress due to the cutout. However, I was wondering since we are essentially removing area from the structure wouldn’t the tensile capabilities on the structure also be affected? Is there a relationship between tensil and shear capabilities of a structure?


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Why are there different bracket shapes to Class D airspace?
A Class D airspace ceiling is typically depicted with a two digit number surrounded by four brackets depicted below.

Why do some Class D airspaces have the same four brackets, with four additional lines within those bracket lines. I've checked the chart user guide and it shows an example of it but that example isn't consistent with airports across the US. Picture below.

As you can see, where it says [32], there are only four right angles around it, whereas in the second example, where it says [62] there are four additional lines in between each right angle and I can't find an answer anywhere.

Surely class D is just depicted with a number surrounded by a dashed line, and the number of line segments will depend on the zoom level?

@60levelchange -- how do you zoom a paper chart?  PS most on-line products you find are just digital copies of the paper charts, or at least of their actual map portions, i.e. some exclude the margins and the information contained therein.

The FAA's Chart User Guide clearly says "Class D Airspace is identified with a blue dashed line." on page 17, and on page 27 it shows examples with four and eight blue dashed segments. The eight segments example is used in a bigger box, the four segment example is used in a smaller box. No contradictions here, the text merely says "Class D Airspace is identified with a blue dashed line." which is clearly the case in both examples.

Suggested edit-- something to the effect of "In general, bigger boxes are used in larger areas of Class D airspace, or when three characters need to be enclosed, e.g. when there is a "-" sign."

@quietflyer: "larger areas of Class D airspace" would refer to the airspace itself. The four vs. eight segments question has nothing to do with the airspace size but with the sized of the displayed box.


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Are Holding Speeds Regulatory?
Throughout instrument I was taught the three different holding speeds (e.g. 0-6,000' MSL is 200 KIAS) and now that I'm starting CFII I am curious about what regulation someone would be breaking if they were to exceed that maximum. The only two places I could find these speed limits are the AIM 5-3-8 and the Instrument Flying Handbook which in the handbook it references the AIM. The AIM isn't regulatory, it's essentially a guide book the information pertaining to basic flight information and ATC procedures. FAR 91.117 is the primary regulation for aircraft speed. However, it doesn't discuss these holding speeds. So, if someone were to fly above this speed, would they simply be making ATC's job harder, or would there be repercussions to them exceeded said limit and what would the regulation be? Thank you!

The holding area (protected airspace around the holding) is calculated based on the holding speed. If you exceed the designated holding speed, your holding pattern will be larger than expected, and you may inadvertently lose obstacle clearance, enter restricted airspace or end up conflicting with nearby traffic.

The regulations that cover holding patterns are covered by 14 CFR §97 Standard Instrument Procedures, specifically Subpart C-TERPS Procedures:

§ 97.20 General.
(a) This subpart prescribes standard instrument approach procedures
and takeoff minimums and obstacle departure procedures (ODPs) based on
the criteria contained in FAA Order 8260.3, U.S. Standard for Terminal
Instrument Procedures (TERPs), and other related Orders in the 8260
series that also address instrument procedure design criteria.

Subparagraphs (b) and (c) go on to specify that the published procedures are incorporated into this part by reference. But specific to holds, it is beneficial to refer to the TERPS, currently Order 8260.3F Chapter 16 Basic Holding Criteria, which covers the design of charted holds.
Of particular interest to this question is section:

16-1-8. Air Traffic Operations. ATC assumes responsibility for obstacle clearance when giving authorization for an aircraft to hold
at other than a charted holding pattern, above the maximum altitude
considered in the holding pattern design, or at airspeeds above those
considered in the design. When depicting holding pattern airspace
areas ATC will only use the primary area.

And the following section provides more detail on holding airspeeds:

16-2-3. Maximum Holding Airspeed.
a. Develop holding patterns based upon maximum airspeeds of table
16-2-1, with the exception of Increased Airspeed Holding Operations
defined in section 16-12. Holding patterns developed at other than the
standard airspeeds must be annotated in order for pilots and
controllers to know that either slower airspeeds are required, or
higher airspeeds are allowed.
Table 16-2-1. Maximum Holding Airspeeds
Maximum Holding Airspeed through 6000 feet | 200 KIAS
Above 6000 feet through 14000 feet | 230 KIAS
Above 14000 feet | 265 KIAS
Note: At USAF airfields, the maximum holding airspeed is 310 KIAS
unless otherwise noted.
At USN airfields, the maximum holding airspeed is 230 KIAS unless
otherwise noted. Annotate procedures at Joint-Use airports, designed
to accommodate increased airspeed holding, since military airspeeds
cannot be assumed.
b. Where operationally necessary, restrict civil holding patterns to
the following speeds when the procedure has the restriction annotated:
(1) 175 KIAS at altitudes from MHA to 18000 feet MSL, as part of an
instrument approach procedure that is restricted for use by CAT A and
B aircraft only. A 175 KIAS holding pattern is non-standard and is
highly discouraged. Development of 175 KIAS holding patterns  must
only be accomplished to avoid obstacles and terrain.
(2) 210 KIAS at altitudes above 6000 feet through 14000 feet MSL.

In the US, there are no regulatory speed limits for holding patterns, in general, only for IFR. However, keep in mind:

The FARs are not the only way to prescribe regulatory mandates. People oftentimes believe that just because something is not in the FARs, there is nothing in "the regs" (whatever that is supposed to mean). The FAA can still mandate things for you outside of the FARs.
There can still be FAA-prescribed speed limits in specific cases, for example some IAPs have charted holding patterns that have a non-standard speed limit written inside the racetrack or outside of it. That is now mandatory for you, because it is published on the IAP.
"The AIM is not regulatory". Two points on this. a) The AIM includes many regulatory items, so you can not construe this as "nothing in the AIM is regulatory". Yes, the regulatory items, for example, are regulatory, despite them being in the AIM. b) If you deviate from the AIM or other FAA sources, for example ACs, in a "wild" manner, you cannot simply say "That's not regulatory". You should then be able to explain that you had good reasons to deviate from the AIM or AC, and explain these reasons. If you can, it's all good, the FAA will agree with you and attaboy you for superior judgment. But you cannot construe "not regulatory" as willful disregard or laziness or "just don't care". You can always deviate from the norm with superior reasons, but it's not a free-for-all to defy the rules. It could also be seen as a hazardous attitude (macho) or a violation of 91.13, careless and reckless.
Another example of regulatory despite not being in an FAR is the TPA. People sometimes think they don't have to obey the TPA because it's not in the FARs. But it's published in the AFD. So now it's regulatory.
More examples of regulatory despite not being an FAR are the official letters of interpretation form the Chief Counsel's office. There are several of these, one I happen to remember is that it's only the pilot's prerogative to determine the visibility if there is no ground-reported weather. If there is, you are bound by it, regardless of what you think the vis is.
By logical conclusion, although I have never seen any reasoning along these lines, is that regulatory despite not in the FARs should also be decisions by the administrative law judges. Their decisions are binding, also against the FAA, so that would be another source for binding despite not in the FARs. And I think this may get interesting in the future, Thomas and Gorsuch have indicated they want to overturn the Chevron Deference, that means conceivably there could be more action against the FAA in courts than before, with more cases decided by ALJs becoming permanent law. But that's speculative on my part.
You are referring to 91.117 although you also mention an IFR context (are working on your CFII, refer to the IFH, etc.). You correctly say that 91.117 is the general speed limits, and say that it says nothing about holding pattern speeds. You cannot expect much there in 91.117 for holding patterns. VFR holds don't happen a lot, and they don't require lateral or speed limits, because it's VMC. What makes holding interesting is in IFR / IMC. So you should expect more in the IFR section of part 91, which starts at 91.167. Keep in mind, specific always supersedes general. So anything about speed limits in IFR holds couldn't be in 91.117, it couldn't possibly be in anything below 91.167.

In short: there are regulatory sources outside of the FARs, these include: AFD, ACs, letters of interpretation, charts, and (I believe) ALJ decisions.
Would also be careful to disregard the FAA manuals, including, but not limited to, the AFH, IFH, AIH, PHAK, Chart User's Guide, Mountain Flying Handbook, etc. The FAA can't fault you for being in compliance with their own publications, but that also means you shouldn't grossly deviate from them without good reason. I personally think these handbooks are even much better than the AIM and have better explanations and better illustrations. Also some of the newer ACs are extremely good, such as the one about avoiding wake turbulence after departing aircraft. After the damage you can't say "didn't read that AC".

can you cite a reference for your claim that the FAA can regulate outside of 14 CFR? Your assertion that a non-standard holding speed limit is regulatory because it is published on a chart is incorrect.

@Timbo: Are you saying NOTAMS, TFRs, ACs, ADs, etc. are rooted in the CFRs? If they are I am willing to rephrase.

@AndreasLauschke yes. NOTAMs and TFRs there are sections that say "the Administrator will issue NOTAMs in case of blah and you can't operate within the area designated by the NOTAM unless mumble". ADs there's a section that just says "ADs are part of the CFR."

@hobbs: Thanks, I have rephrased.

Re "The AIM is not regulatory". Two points on this. a) The AIM includes many regulatory items, so you can not construe this as "nothing in the AIM is regulatory". Yes, the regulatory items, for example, are regulatory, despite them being in the AIM." -- this is what is known as a "straw man" argument. The people who say "the AIM is not regulatory" do not mean that the AIM contains no information about regulations. They certainly do not mean that if something is in the AIM, then it cannot also be in the regulations!

Rather, they mean that something that appears in the AIM but not the actual regs should not be considered regulatory.

Re "b) If you deviate from the AIM or other FAA sources, for example ACs, in a "wild" manner, you cannot simply say "That's not regulatory". You should then be able to explain that you had good reasons to deviate from the AIM or AC, and explain these reasons."   AC's, maybe, if they are specifically clarifying the intent and purpose of regulations.  But in general the FAA cannot regulate a pilot's actions simply by printing stuff in AC's or in the AIM.  That's not the way it works.

Case in point: AIM 3-2-6(e)(2) contains the following phrase: "Surface area arrival extensions become part of the surface area and are in effect during the same times as the surface area." -- should a pilot be prepared to hang his career on the idea that this should be treated like a regulation?  If an "extension" becomes "part of" the core "surface area", then all regulations pertaining to the core "surface area" must also pertain to the "extension", right?  So...if a SVFR clearance may be granted for the core "surface area", it may also be granted for the "extension", right?

But... https://aviation.stackexchange.com/a/56045/34686... oopsie! And see also the "Gardner memo"-- https://jrupprechtlaw.com/section-107-41-operation-in-certain-airspace (scroll down) -- which holds that Part 107 treats surface-level "extensions" fundamentally differently than core "surface areas" in context of commercial drone operations. The ultimate answers to these quandries are still in flux-- but no one is seriously going to say that all statements in the AIM should be treated as if they were regulations.

There are still several false statements in this answer that need revising. The AIM is not regulatory, full stop. Second, holding pattern speed restrictions are a TERPS created value, charted to indicate that the obstacle protection is not standard. It is not a speed restriction in the regulatory sense. Procedure forms, the legal record for Part 97, do not contain holding airspeeds (other than those to be charted). Holding data is found on 8260-2 forms, which is not covered by Part 97. Third, legal interpretations are interpretations of the regulations, not the creation of a regulation.


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Landing Currency for Type Rating Airplanes
When discussing landing currency, we need three takeoffs and landings within the preceding 90 days in the same category, class, and type of aircraft to be flown. Type meaning type rating and not just 172 vs PA28. I understand if you do your landings in a Piper Seminole (AMEL) you're not current in a 737. However, if you're type rated in the 737 and do your 3 landings in the 737, does that also count for your currency for the Piper Seminole. Like would the currency for a plane with a type rating count for the plane without a type rating given they're the same category and class? It feels silly to ask but just want to make sure.

Yes.  If you are landing current a B737, you will also be landing current in a non-type rating AMEL aircraft as well.


text:
Can you circle beyond the published circling radii?
The FAA's TERMS/LANDING MINIMA DATA establishes a radius from each runway complex as airspace that is protected depending on the category of aircraft as specified in FAR 97.3. Is this circling radius a regulatory requirement to only circle if within that radius or can you begin the circling maneuver so long as you have the runway complex in sight regardless of your distance from the runways? If it is regulatory must you execute a missed approach if you find yourself outside the protected airspace as defined by the radius even if in visual conditions? Please provide FAA references, thank you!

Given that circling is already a not-ideal way to interact with an airfield, if you've got visual contact with the field at greater distance... why not just make a visual approach? If you really wanted to circle with that kind of visibility you could also just cancel IFR and proceed to enter the pattern for your desired runway?


text:
Why isn't the rudder below the tail?
Most airplanes have a rudder on top of the tail. When it is turned to the left, it causes the plane to yaw to the left. But it also puts a roll force to the right, because it is usually above the center of gravity. Of course, this force is smaller, as the leverage is much shorter. Still, this is not logical to me. Wouldn't you want a roll force in the same direction as the yaw? Or at least no roll force at all? It would be more logical to me if the rudder was below the center of gravity. Why isn't this usually the case? Is there a name for a rudder below the tail?

If it was below the CG it would be much more prone to scrape the ground.

The Dornier Do 335 Pfeil had a rudder below the elevator (mainly to protect the rear prop from groundstrikes). This required long stalky landing gear, which was troublesome throughout the type's service life.

The plane needs to rotate up in order to take off. Plenty of missiles have rudders on both sides.

The X-15 had a symmetric tail while in flight; part of the landing procedure was to jettison the lower tail to gain sufficient ground clearance.

Shenyang J-8II also have a sizable vertical tail on the under side.

What we are talking about here is the vertical stabilizer, and yes, it can be below the tail, as seen in a common paper airplane.
But the position of the tail is not the only factor in creating a roll force in the same direction as the yaw.
Let's start out by making the plane stable in roll first.  If the plane is tipped to the side by a wind gust, how can we design it to roll itself back to upright?
It's important to realize that once a plane rolls, the wing produces less vertical lift, and the plane will start to sink.  This puts more wind flow on the downward facing side.
If the vertical stabilizer area is above the center of gravity then the plane will tend to roll back upright.  Wing dihedral also helps do this.
So how do we create a roll force in the direction of the yaw?
By overcoming inherent roll stability with ailerons.  This is called "coordinating" the turn.

Designers try to balance between excessive stability and the ability (when desired) to roll, pitch, and yaw the aircraft.

If you just push the rudder, where is the wind flow?
Now it's on the other side, pushing the dihedral into the turn!  We can see the dihedral produces a roll torque and the (upright) rudder produces an opposite roll torque.

this helps prevent the need for opposite aileron to "hold" the inside wing up

In design, it's far safer to have the inside (turning) wing aileron up and the outside wing aileron wing down, as this lowers the AoA of the inside wing.
So much for rudder turning, how do birds "do it"?
They pull the inside wing in and slip turn.  Here, it is advantageous to have the Vstabilizer/rudder down, because now wing dihedral rolls away from the turn.
So much for the birds, how do most airplanes want to turn?

the best way to turn is coordinated, with the airstream as close to parallel to the direction of flight as possible.

This means that after the rudder is applied in a coordinated manner with banking (rolling) the aircraft, and as the aircraft begins turning, side forces drop to a minimum.

the rudder and vertical stabilizer can be up or down

For practical reasons involving tailstrike, they are usually up. The Junkers Ju-187 was actually designed to have its tail rotate from "upright" to downward in mid-flight.
Finally, there is a device that creates roll and yaw in the same direction known as a spoileron, mounted on the upper surface of the wing.  The spoilerons acts to create yaw (by drag) and roll (reduction of lift) on the inside turning wing.  Essentially, it is half an aileron.

Moving comments to chat room https://chat.stackexchange.com/rooms/150014/a-room-to-discuss-ase-question-why-isnt-the-rudder-below-the-tail

It is bad to put things below the tail because they might hit the ground.  Even with nothing below the tail sometimes there is still a tail strike.

http://avherald.com/h?article=42b2d053

The MQ-1 Predator does have a V-tail ruddervator below the tail.
Does the Predator drone's design make a tail strike more likely on takeoff and landing?
The MQ-1 is already at high risk of a rear propstrike.  As a result, there is not much disadvantage to inverting the ruddervator.
More on V-tails: Why are military drones shaped so strangely?

The rudder might be more tolerant to a ground strike, than the spinning prop.

Why isn't the rudder below the tail?

Compromises, as usual in the aerospace world.

From an aerodynamic and flight mechanics point of view the best location for the vertical tailplane would be aligned with the centerline of the fuselage, i.e. sticking out both upwards and downward. This would give a pure yaw moment with the deployment of the rudder without any cross coupling with the roll movement, as you have correctly highlighted.
Something similar has been seen in the past, like for example the Douglas XB-42:

In that case the lower part of the vertical stabiliser had the additional work of protecting the propeller from striking the ground. This kind of tailplane is normally termed cruciform.
Ok, but what about taking off? When the takeoff speed is reached, the AoA of the wing has to be increased to get enough lift to takeoff. This manoeuvre is called rotation and it makes the bottom of the fuselage almost scratch the ground (A380 image source):

If a vertical tail were there, the rotation would be possible only with very long landing gears: the XB-42 had indeed relatively long landing gear and "careful handling during taxiing, takeoff, and landing was required because of limited ground clearance. An integral shock absorber was added to the ventral fin to reduce excessive bending force in the tailcone from a ground strike".
This solution might work for a small airplane but not for a jetliner: longer landing gear means higher weight, bigger space needed  in the wing for retraction (instead of fuel) and higher stairs to board the airplane. Everything is a no-go and so, as a compromise, a vertical tailplane sticking out only upward is used in exchange for some (very small and perfectly controllable) yaw-roll cross coupling.

Note that a similar reasoning applies also to the wing: the best location would be just in the middle of the fuselage i.e. not high like in a cargo, nor low like in any jetliner. But then the wing structure would cut the fuselage from side to side in half, splitting the aisle in a separate forward and rearward section.

"This would give a pure yaw moment with the deployment of the rudder without any cross coupling with the roll movement" There's an advantage to roll movement; generally one wants to bank during turns.

Ventral rudders that extend below the vertical C of G have a plus, but a minus.
The plus is rudder application imparts a roll toward the slower wing when yawing, similar to dihedral effect, but which doesn't require sideslip to get started to work. You could say that the rudder's effect as a big aft-mounted aileron is harmonized with its yawing effect in providing a desirable rolling reaction to a yaw input.
On the other hand, sideslip's action on the fin imparts a roll into the slip, counteracting wing dihedral effect (which requires sideslip to be present to do its thing) and increasing its tendency to spiral.
In practical terms, a good dihedral effect is more desirable that a favourable roll-yaw couple, so this favours the rudder above, which also has all the obvious  packaging configuration advantages. So under slung rudders are rare.
A couple of cases that come to mind are the Lesher Teal and Molt Taylor's Mini IMP.  Molt used to promote the sympathetic roll due to yaw effect as a feature of the inverted V tail.


text:
Can I get a UK Civil Aviation Authority (CAA) issued Class 1 medical with monocular vision?
I was born with no central vision in my right eye, and I would like to know if this would hinder my ability to become a commercial pilot.

See here information from the UK Civil Aviation Authority (CAA) and information I found on Wings Taking Flight:
CLASS 1 - AMC1 MED.B.070
(f) Visual acuity

(1) Reduced vision in one eye or monocularity: Applicants for revalidation or renewal with reduced central vision or acquired loss of vision in one eye may be assessed as fit with an OML if:
(i) The binocular visual field or, in the case of monocularity, the monocular visual field is acceptable;
(ii) In the case of monocularity, a period of adaptation time has passed from the known point of visual loss, during which the applicant should be assessed as unfit;
(iii) The unaffected eye achieves distant visual acuity of 6/6 (1,0) corrected or uncorrected;
(iv) The unaffected eye achieves intermediate visual acuity of N14 and N5 for near;
(v) The underlying pathology is acceptable according to ophthalmological assessment and there is no significant ocular pathology in the unaffected eye; and
(vi) A medical flight test is satisfactory.
Fit with an OML means valid only as or with qualified co-pilot.


text:
What is MZFW and what will happen if an airplane exceeded this weight?
What is MZFW and what will happen if an airplane exceeded this weight?
Is that the wing root experiences the highest bending moment under the loading condition corresponding to Maximum Zero Fuel Weight (MZFW)?
or
According to Boeing W&B study.

I am truly confused about those concepts.
Are those concepts different between GA and transport category due to GA without center fuel tank?

What is the source of the slides presented here?

What is your doubt exactly? The naming convention? The plot of the moment? The fact that the center tank is filled after the wing tanks?


text:
Air regulation. About QNH , TA and TL

What is the TL here ? How to calculate this ???

Transition Level, is the altitude where you switch from standard pressure to the altimeter setting while in descent.

There has to be more to the question than what is shown?  What is the standard transition level over Mumbai?

Please enter the text into your question instead of depending on screenshots.  People using accessibility services may not be able to read text within screenshots.  Thanks!

Questions in the format of "answer my homework question" showing no effort on the part of the OP are not appropriate on Aviation.SE.


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what are the compression forces in a strut if the strut is fixed
i am trying to match an experiment i have done and i dont know how to compute the force in the strut in terms of F given these boundary conditions. i have attempted to use fixed end moment equations but cant find anything suitable, can anyone help as to why this might not work or how it might work?

This looks a lot more like general engineering than about Aviation. Note that on the ground, the weight of the wing is the net down-force, but in flight, the wing is lifting with enough force to equal not just the weight of the wing but the weight of the entire aircraft (distributed over both wings), so the strut would no longer experience compression, but tension.

F will actually be located at the spanwise center of lift, in the up direction, somewhere just inboard of mid span. If you place the strut attachment at a sweet spot, which depends on the elasticity of the wing spar, you can arrange it so the load on with wing root is reduced to zero in the vertical axis with only a lateral compression load. The vast majority of the lift is being borne by the strut in tension. The 3 attachments are always pin joints. On a Twin Otter, which has a lot more span outboard than inboard of the attachment, the load on the wing root fitting is DOWN plus compression.

@RobertDiGiovanni where did you get the 2F from?

@mwtb123 from F at the wing tip.  The actual load may be distributed across the entire wing, resulting in most of being supported by the strut (as 1F).  See JohnK comment above for the (excellent) real world story.

Is the wing-"strut" connection a hinge or fixed?

That would indeed be the common way of doing it Robert. However, the question specifically states that the strut is fixed (not a pin joint!) at the bottom left. So then it's no longer safe to assume that the connection at the wing is also a pin joint...

This link should help.

In terms of movement (whether pinned or welded) the strut is more or less fixed.  Slight movement (repeatedly) could cause fatigue in a weld.

The practical answer is that, unless your connection with the "wall" is extremely rigid and the "strut" is extremely stiff in bending, the situation can be reasonably well approximated by a pin-jointed strut. However, assuming you really want to know the answer, you'll have to resort to methods for statically indeterminate problems.
For the problem as presented I see no easy shortcut so you'll have to rely on general methods. I would recommend the method of virtual displacements. At the connection point, determine the resulting forces and moment for a virtual displacement dx and dy and rotation drz. Do this for both the strut and the left hand side of the wing. The strut will have longitudinal stiffness and bending stiffness due to a end force and moment load. Easy enough to calculate in the strut frame of reference, and afterwards just decompose the resulting forces in the global frame of reference (moments are unchanged). The left side of the wing has longitudinal stiffness and bending stiffness due to a moment load.
Add up all the forces with each virtual displacement. Equate with the force and moment due to the force at the hinge point. That gives you the actual displacements. Finally, from these displacements calculate back the force at the strut. Basically you've done a FEM analysis by hand.
Now redo the analysis for the much simpler pin jointed strut and realise you've gone through a lot of effort for a marginal difference in results. Note that the strut is not infinitely rigidly attached at the wall (quite the opposite typically) so even this small difference disappears.


text:
Is the front wheel supposed to turn 360 degrees?
Came across this youtube video where a tug does a 180 degrees turn while towing a gulfstream and then at minute 00:50 adds 180 degrees more to complete a 360.
If you notice closely the wheel actually turns with the tug all the time (is not static).
Are airplanes wheel structure supposed to behave that way, and can you as well turn the wheel 360 degrees from the cockpit?

Note how the wheel steering linkage (arm) has been disconnected:

The wheel freedom is limited to about 80°, the arm must be disconnected in order to go further. In this video, while this disconnection is neither shown nor commented, you can see the arm connected at 0:43 and disconnected a second later.
This 80° limit is for a good reason:

You can see only one tire would touch the ground at 90°. The wheel actually stands on the tug platform, the tug supports the aircraft weight while turning.
Note how the lower part of the wheel jack has turned, but the upper part didn't. The disconnected arm moves with the wheel, but the arm anchor points position hasn't changed. They are in the position last commanded from the cockpit.
Details of the cradle and turntable from Lektro:

The operator disconnects the arm, hooks the wheel with the yellow U-hook, moves the wheel onto the turntable and locks it by retracting the hook with the flat strap.

Some airplanes have nose wheen steering, some do not.
Nose wheel steering does not allow the nose wheel to turn full 360 degrees, unless the steering system is disconnected from the lower assembly. It should be noted that not all freely pivoting nose Wheels can turn 360 degrees there may be limiters/limitations in the system preventing this.
In the planes with freely pivoting nose wheel the steering is achieved by differential braking such that the pilot applies brakes on either side of the plane to make it turn.this is not as convenient and precise as a nose will steering.
As a rule of thumb: the smaller the plane is the less likely it is to have a steerable nose wheel. This is because the system adds complexity and weight

I highly doubt that a Gulfstream does not have nose wheel steering at all. More likely they can disconnect the nose wheel steering during tow operations. Can you add a source?

The G450 AOM (from this site) says: "The nose wheel steering linkage must be disconnected for aircraft towing by removing the connecting pin on the torque link between the actuator and the nose wheel." Interestingly, it also says "Care should be taken to ensure that the nose wheel is not pivoted in excess of the 80° limit." No idea what they were doing in that video.

@Bianfable thanks, I stand corrected!


text:
Is there such a thing as icing in the propeller?
It is well known of the fatal effects that can have ice build up on the wings, causing loss of lift and the multiple fatalities that have occurred due to this trough the years.
I was thinking though, if besides the wings, there were other aircraft parts where icing can build and have critical impact on the aircraft, more specifically thinking about propellers in airplanes.
Is there such a thing as icing in the propeller?

Related How do electric anti-icing systems work?

For sure. Ice tends to collect toward the blade roots (the outer blades and tips are moving fast enough for compressibility heating to keep the leading edges from accumulating ice) and spinner, so on turboprops you usually see electrically heated rubber boots on the slower moving inboard part of the blades. Ice on the spinner just accumulates until it gets flung off by centrifugal force.
Look at many large turboprops and you'll see a funny looking overlay panel on the fuselage beside the propeller. They are shields to protect the fuselage from ice pieces shed by the propeller and spinner, which can make dings in the aluminum like hail damage.

If centrifugal force is strong enough to fling ice off of spinner, why isn't it strong enough to fling ice off of blade roots, that are radially further than spinner?

The ice can accumulate as a thick chunk on the blade root because of the way it builds up on the blade leading edge, and the centrifugal loads are in shear, so when it lets go, it's grown into a big piece, and if one breaks off and the others don't, you get a nasty imbalance, aside from the chunk hitting the fuselage. On the spinner it's more of even sheet that flakes off in small pieces.

Yes. Many prop planes use electric heaters in the blades which are cycled on and off to maintain the blades in an ice-free state, while the plane is flying through icing conditions.
In the piston-powered DC-7, the galley and rest room were positioned in the rotation plane of the propellers to reduce the chances of killing someone if one of the engines threw a blade through the fuselage- and there was a little round window in the rest room. If you were in the rest room when the de-icers came on, you could peer out that window and see the blades of the nearest engine throwing off little splurts of slush that would then strike the window.

There are any number of info links for prop icing.
https://hartzellprop.com/what-to-know-aircraft-propeller-ice-protection/

Ice typically appears on propeller blades before it forms on the
wings, so it’s important to address propeller icing as quickly as
possible.

https://ntrs.nasa.gov/citations/19810068625
The Effect of Ice Formations on Propeller Performance
https://uavicinglab.com/2024/01/09/new-advancements-in-ice-protection-systems-for-uav-propellers/

The NTNU UAV Icing Lab, together with Mejzlik Propellers, and UBIQ Aerospace have developed a system to protect the propellers of UAVs when flying in icing conditions.


text:
Help geo locate this specific spot
I came across this picture online and the info I could obtain is that it is near the Taipei Songshan Airport.
However I couldn't find the specific spot on google maps. Any idea what is the specific spot? I would like to take that picture one day.

It's literally written on the picture. 北安路458巷, the green sign on right side. Copy this into google map: 10491台湾台北市中山區北安路458巷

No comprehendo Chineso!

With a bit of digging around on Google maps, I was able to find the distinctive red cables of that bridge, and identify it as the Dazhi bridge - just north of the airport. Note that this shot was taken with a long telephoto lens, so you'd need to go some distance further up the road to get a matching angle.


text:
Do wheels continue spinning when gear retracted?
Do landing gear wheels continue spinning inside the landing gear compartment once the gear has been retracted or is there a mechanism that will stop them?

Some aircraft have little friction skids that slow the wheels down, especially on nosewheels where there are not normally brakes.
On main and body gear, the brakes are (automatically on larger aircraft) momentarily applied during the retraction process to stop them from rotating.

They continue spinning but there is a simple friction mechanism that immediately stops them. You can see how it works in this video at 10:50.

license: Creative Commons - Attribution Share-Alike - https://creativecommons.org/licenses/by-sa/3.0/


text:
What factors are considered when a runway is planned?
What environmental factors are considered when a new runway construction is planned (e.g. winds, weather, sun direction, etc.)?

They look for a spot where there are as many spotted owls as possible.

Have you seen this question? It might answer your question, at least partly.

Section 17 of this book is related to environmental topics in relation with the airport construction / extension.

Runway Orientation. The runway to be constructed shall be oriented that the approach/departure zone will be free from any fixed obstacle (i.e. buildings, mountains, railroads) penetrating the approach/departure area and as far as practicable away from populous area. The prevailing wind directions shall also be considered.

This looks like it has been lifted by some other source. Would you mind providing the source?

It's just common sense. I feel this is not so useful answer but i think it is a valid one.

ICAO Airport Master Plan Manual

all_licenses: Creative Commons - Attribution Share-Alike - https://creativecommons.org/licenses/by-sa/3.0/


text:
Is seating distribution planned in airliners or is it left to casuality?
One thing I have always wondered when taking intercontinental flights is the way passengers are distributed in an aircraft. It seems to me that in some way people of different ethnicities are purposely mixed. I have the strange idea that this is preset and done mostly for security reasons.
Seeking for clarification on this matter. Please do not get me wrong as I am not trying to classify different types of people!

I fail to see what ethnicity has to do with security and I believe that this question may attract the kind of responses we don't need in an international community.  I am therefore voting to close.  Sorry.

That would be illegal --and a huge commercial mistake-- to use ethnicity (or religion, or political choices) data for any distribution purpose in any European Union country, so maybe you are asking about another region.

If it has to be closed please do so. My intention is not to create a flame post.

The question itself is not a problem to me, this is more about the specific link with aviation. It would be a better fit for Travel.SE.

People tend to travel by themselves or in small groups. They sit all over the airplane, either selecting their own seats or having them assigned by the airline's ticketing system. When you go to select your seats, the system shows you what seats are available, but it does not show you other passenger's ethnicities. Airlines also don't necessarily know passengers' ethnicities when assigning seats in advance, except to the extent that they could conceivably guess based on names (they may know what country's passport someone is traveling on, which is not the same as their ethnicity, but even so, they may not know this information until well after a seat assignment is in place).
So lots of people check-in and have their seats assigned basically randomly. The expected result is that small groups of people of different ethnicities would be mixed throughout the plane fairly randomly. I'm not understanding why you think this is something an airline would deliberately need to do, as it would already happen naturally.
Using ethnicity for seating purposes could also violate anti-discrimination laws in many countries, if this was something an airline even wanted to do.
It is sometimes the case that a large group of passengers largely of the same ethnicity will book a block of seats together as part of a group booking, such as a Japanese school trip or German musicians. Such groups may, if space permits, be seated together, and if the group is relatively ethnically homogeneous, you may find a number of travelers of one ethnicity seated together for this reason.

Hi. The question was based purely on security. You know with things that happens these days you might want to split up people in order to avoid surprises. Good answer though.

Given the way seats are typically assigned, how could an airline split large numbers of people up if they even wanted to? Passengers usually have their seats assigned in advance and those assignments generally don't change unless there's some special reason (change of aircraft most often).

As a sidenote, since you seem to think it's a security matter, the 9/11 hijackers were split up, at least within the first class/business class part of the aircraft. These seating charts come from a 9/11 conspiracy website, but appear to be accurate: UA 175, AA 11, UA 93. And there are plenty of innocent reasons why, say, five men of any ethnicity might travel together and wish to sit together.

@FabrizioMazzoni You seem to forget, or ignore, that in the majority of countries, more people are killed by those of their own ethnicity than by others.  Logically, you would want to split up everyone - but that would be impossible.

@Simon Are you implying that homicides regularly happen on planes, and that splitting up people by seating them randomly would be a good solution to this?

I sincerely doubt Simon was implying anything of the sort.

@CodyP  Nope. Just that logic says that you cannot use ethnicity to determine security policy or the probability of being killed.  Travel.SE or Sceptics.SE would be a good place to ask why.


text:
Does a flight cycle require a minimum duration?
For medium/long-haul pressurized airliners that are used on short routes.
How is a cycle calculated?
Wouldn't the short flights impact the maintenance schedule due to the frequency of pressurization cycles?

You may consider several parameters to define a cycle, some of which only occur at take off and landing (landing gear touch down effects on wheels --rotation, break--, engine full thrust, engine start up,...) other only when transitionning from ground level to cruise level (pressurisation, flaps operation, engine at climb thrust for several minutes,...)

What do you define as a cycle?

This question cannot be properly answered unless the type of cycle is defined. Different aircraft have different cycle definitions, including engine starts, pressurization, and wheels up/down. Our operation determines cycles based on engine starts, not pressurization, since engine starts are what our maintenance ops are most concerned about.

If you are talking about a flight cycle, then yes, this does increase maintenance costs. The Zero-G Airbus considers each parabola a cycle for the aircraft and engines and greatly increases maintenance and operation costs.

Much of the wear on an engine happens during startup, so while yes it does have a significant impact on maintenance costs, it's rather unavoidable unless the operator chooses to avoid shutdown between flights (as some do, e.g. skydiving and ag spraying)

A cycle is mainly based on the pressurization and depressurization of the cabin, during these stages the diameter of the fuselage increases and decreases (pressurization, increase in diameter, depressurization, decrease in diameter). The causes fatigue stresses in the material. For the fatigue it is less of an issue what the duration is of the cycle.
For the engines, before takeoff the engines need to reach operation temperature (about 3 minutes after start or faster for newer engines )For the engines the same hold as for the fuselage but here the temperature is responsible for expanding and shrinking of parts.

A cycle is not necessarily a pressurization cycle. Cycle has multiple meanings.


text:
Do captains and first officers always fly together or are they mixed?
I was wondering if the same captain and first officers always fly together for some time as some sort of a team or are they mixed around in every flight? I suppose if you have one plane that is the case but what happens in huge airlines such as emirates? Wouldn't it also be a drawback always flying with someone that you do not actually know?

In airlines where pilots bid on monthly lines it is conceivable that a pair of pilots fly all month together. However, trip trading and reassignments rarely let this happen. It is far more common that a crew only stays together for a single "pairing" that lasts between 1 and 4 days (domestic 121 USA).
It's not a drawback to fly with new people because training emphasizes standard flying according to the FOM. Ideally, every pilot is exactly the same.
  Practically it is close enough that you can drop any two pilots from the same airline into an airplane and they more or less operate it exactly the same way.

Do captains and first officers always fly together? No. For large airlines, it would be the exception, rather than norm to fly with the same First Officer several times in a year. For example, consider KLM- it has less 200 aircraft in its fleet, but well over 2000 pilots. Even making allowance for type certification, there are quite a few pilots for each aircraft.
I doubt there would be any drawback in working with a new FO for the first time. Both are fully qualified to fly the plane in all regimes of flight, and usually do so in alternating turns. As an example, the pilots who landed the US Airways Flight 1549 safely in Hudson met for the first time during that flight, though having enormous experience.

Of course, there can be exception to this rule. For example, only 20 pilots were trained to fly the seven Concorde jets of British Airways and as such, they would've flown together more often than others.


text:
Why are Airbus captain control sticks placed on the left when most people are right-handed?
Why is it that control sticks for the captains on Airbus are placed on the left? Wouldn't it be uncomfortable considering that most of the people, and by consequence pilots, are right handed?
To my opinion this would make flying more difficult as a right handed person would have less sensitivity on his left hand.

(airbus.com)

why only think of right-handed captains? poor left-handed FOs?

True. But according to wikipedia 75-90% of humans are right handed

related: Which hand do fighter pilots use for the control stick? and Are there risks if the side joystick must be handled with a pilot's weaker hand?

My anecdotal experience suggests the incidence of left-handedness is higher among pilots than the general population, but my anecdotes are also strongly biased by the crew members I trained with.

Since this popped back to the top... I steer my car left handed because it's a manual and I shift with my right hand. I steer my wife's car right handed because it's an automatic and my right hand gets bored without having something to do. I don't have problems wobbling from lane-to-lane in either vehicle.

Even just in an automobile (manual gearbox), anyone who spends a lot of time in countries with the both LHD and RHD ... it's quite mysterious that there is almost no difference in having your left or right hand on the gearstick.  For some reason it's quite natural to control the gearstick, with either hand, even if you've never used that hand on the gear stick before. Strange thing!

Being right-handed merely means that you write more easily with your right hand.  It's perfectly possible to be a righty who controls a joystick better with one's left hand than with one's right.

I'm left handed and I can tell you, that I can use right handed joysticks about as good as left handed. It's just a question of training. What's worse would be having the stick in the way when trying to reach controls in the center of the aircraft in a critical moment. So moving the sidestick to the outside removes the possibility of accidentally hitting or moving the stick when you want/need to reach controls on the centerline.

Since this popped back to the top... again... Most console video games use the left thumb stick for steering and the right thumb stick for changing view (or other things). To be fair, I've never mastered the left-thumb steering, but both my left- & right-handed sons can steer leftie and view rightie with no issue.

The Airbus is actually configured the same as the vast majority of other General Aviation and Civil Aviation aircraft.
The key factor is that the throttle is almost always the middle - meaning that  as pilots get used to sitting in the left seat early on in their training, they become accustomed to using the throttle with their right hand and the control column in the left.
It's something of a misconception to think that pilots spend much, if any, time with both hands on the control column. The right hand is almost always somewhere else – configuring radios, squawks, navigation equipment, throttles and so on.
Watch this video of a Citation Jet – particularly during takeoff and landing.

The pilot on the left is using his control column in exactly the same way as he would on an Airbus. You'll note that when his right hand is on the control column, it doesn't become dominant – it's just a resting position.

Well on the J-3 the throttle is on the left and the stick in the middle.  I think there are bigger human factors concerns.

First, even if the aircraft is controlled using a yoke, the pilot is still controlling using his left hand (left hand on column, right hand on throttles/PCL). This is not much different and almost all pilots switch from controlling using their right hand to left hand pretty easily (they'll usually do this while training itself as they switch seats). The basic concept is same as say, a Boeing 737.

Boeing 737 cockpit, from gearthhacks.com
The basic control layout in airliners is that the pilot/copilot controls the yoke/sidestick with one hand and throttles/TCL (and flaps etc.) with the other hand. Having dissimilar layout for pilot/copilot has some advantages.
At the minimum, the throttles can be placed in the center. If the pilot's sidestick is to (his) right, then the throttles have to be placed in the left, resulting in duplication. This can be seen in the B1 Lancer, where the pilot's throttles are in the left (though the aircraft has a centre stick).

Image from left wingsovereurope.com
While this may be possible if only the throttles were to be duplicated, it is very difficult to do so with the whole center console.
Also, having the sidestick to the left side serves as a good hand(wrist) rest.

and that brings up a whole new question - why in the world did they duplicate the throttle quadrant on the pilot's left in the B1? (Yes, that's for a whole new question, not the discussions here...)

F-111 had the same left hand throttle quadrants (for both crew). The quadrants were slightly different, but the ergonomics were very similar.

Please note the flying captain could be left seated or right seated, also the stick on Airbus needs no effort to move it, it is very soft to handle it has a springy central positions. In normal flight longitudinally once you reach the desired vertical speed you may leave the stick, similarly laterally once you get the desired bank angle you can leave it until you finish the turn, so no effort is applied to the stick. What follows explains how this is possible: Indeed longitudinally it gives a LOAD FACTOR order(to simplify this is the ratio of lift to weight), when left in its neutral position it gives a load factor of (1)thus keeping the active path. Laterally it gives a « rate of roll » order, that is when you get the bank angle you want you leave the stick in the neutral position; to get out of the  bank, you move the stick in the opposite direction. So it is a different technology you cannot compare it to a standard control column. Whether right-handed or left-handed, whether the left seated or the right seated is flying it would make very little difference to operate this soft stick.

Well, it would be hard to put it anywhere else! The pilots are used to flying this way. Most captains and left-seat pilots use their right hand on the throttle and left on the yoke or stick during takeoff. The force on these flight controls is minimal, so there's no need to use your dominant hand to fly the plane.


text:
Is this the right procedure to make your way to the door for an evacuation?
After watching this video of an evacuation training and the hilarious recreation of the youtuber on the second part of the video, I couldn't help but think about this seriously, it just doesn't look right to me, it just looks like the FA is going to hurt someone(specially in a situation with urgency and poor visibility: smoke in the cabin, loss of ambient light, etc)
Is that the right procedure?

Yes, this is the correct way, although some variations exist depending on training.
First of all you must realize that the first and foremost task of cabin crew is not to serve meals and beveages. What majority of their training aims at is them basically being able to act as an efficient riot police task force when the doodoo hits the fan.
In the video in question the FA quite efficiently uses both aural and physical language, accompanied by good eye contact. The purpose of this combination is to establish dominance in the panicking and irrational passengers to ensure they can be managed and safely evacutated.
And in case you are wondering: yes, she will jab you with the elbow if you don't make way.

Understood, didn't knew that elbow technique was part of the oficial training. It does make sense to use it to put in their place the ones that go irrational, I just thought there was something more 'friendly'/less aggressive yet at the same time efficient.

@Gabe in non-emergency situations the cabin crew will be polite. For example an unexpected but not time critical disembarkation would be one. But in a real emergency, efficiency will kick the manners out of the plane. They need to have your full attention and compliance and they certainly have the means

Are you sure? I mean, yelling "outta my way" continuously, and hitting non-compliant passengers with her elbow? Also, she doesn't look too calm to me; I sense a bit of a panicked expression, although I may be mistaken.

@AircraftEnthusiast007 yes I am sure.


text:
Can you pay a pilot to take you on a flight if you are the owner of the LSA?
Are you allowed to pay a pilot (whether a Sport Pilot or a Private Pilot PPL) to take you on a flight if you are the owner of the LSA aircraft the flight is being done?

This answer also answers your question: https://aviation.stackexchange.com/a/102240/66887

No. Unless one of a few exceptions apply, private pilots cannot be compensated for their services. In fact, they can't even fly you for free. Giving a private pilot free or discounted flight time in your plane is considered to be "compensation" by the FAA, and private pilots are not allowed to act as PIC for compensation or hire per 14 CFR 61.113(a):

Except as provided in paragraphs (b) through (h) of this section, no person who holds a private pilot certificate may [...], for compensation or hire, act as pilot in command of an aircraft

None of the exceptions are likely to apply here, but even if they do, a private pilot with passengers is required to pay at least a pro rata share of the expenses per 14 CFR 61.113(c):

A private pilot may not pay less than the pro rata share of the operating expenses of a flight with passengers, provided the expenses involve only fuel, oil, airport expenditures, or rental fees.

Meaning even if one of the exceptions apply, a private pilot has to pay for at least half (or 1/3 with 2 passengers, etc. But of course LSAs can only carry one passenger currently) the fuel, oil, and airport expenditures.
Sport pilots are totally forbidden from receiving compensation for acting as PIC and so even this cost sharing is not allowed.
Paying a commercial pilot to fly you in your own airplane is legal.

Ok, Can I also pay a comercial pilot to fly me in my airplane if the airplane is a LSA?

@Gabe Yes. If you pay someone else to fly you in your plane, the plane is not being operated for compensation or hire. So it being an LSA is irrelevant.

No
That would be a violation of 14 CFR 61.113:

(a) Except as provided in paragraphs (b) through (h) of this section, no person who holds a private pilot certificate may act as pilot in command of an aircraft that is carrying passengers or property for compensation or hire; nor may that person, for compensation or hire, act as pilot in command of an aircraft.

P.S.  This topic has been beat to death all over the internet, please do some basic research before posting a question.

Small detail- the aircraft is not carrying passengers for compensation or hire. So it's actually the next clause "nor may that person, for compensation or hire, act as pilot in command of an aircraft" that actually forbids the described operation. These separately forbid a private pilot from acting as PIC (even for free) when the operator is being compensated (first clause) and from receiving compensation themselves (second clause).

@Chris, good point, thanks!  Made an edit above...

@Chris, is that downvote yours by chance?  Because I acknowledged your point and fixed it...

It is not. Honestly my point was pedantic enough I don't think it would be worthy of a downvote even if you refused to fix it. ;)


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Does parasite drag affects stall speed?
Simple scenario, an airplane with landing gear retracted (less drag) vs the same airplane with landing gear extended (more drag).
Are the stall speeds different on each case?

By and large no.  Sometimes there can be a slight interference effect from things like the landing gear doors and the flaps.
However, this is not due to the drag, it is due to other aerodynamic effects.
When landing, you generally want drag -- it helps a clean aircraft descend in a controlled manner.
When taking off, you don't want drag -- you want to be clean to accelerate and climb as quickly as possible.
For this reason, you usually only use partial flaps on takeoff -- enough to improve lift, but with minimal drag increase.  You also try to clean up (raise the gear) promptly after liftoff.
However, on landing, you go to maximum flaps -- a little bit more lift, but a bunch more drag.  You also put the gear down nice and early, so you can verify that they're down and locked -- and so you can stabilize your approach with the drag already out there.
Edit:
Stall speed is a function of the maximum lift coefficient of the wing / airplane.
$V_\mathrm{stall}=\sqrt{\frac{2\,W}{\rho\,S\,C_{L,\mathrm{max}}}}$
So, things that change $C_{L,\mathrm{max}}$ will change stall speed -- primarily, this means high lift devices -- flaps, slats, spoilers.
A wing that is covered with ice will likely have degraded $C_{L,\mathrm{max}}$.
On a variable-sweep aircraft, it would also mean the wing sweep angle.      You might also track a change in wing area with variable sweep.
On a blown-wing aircraft (like the C-17), it can also change with throttle setting.  Paradoxically, with a blown wing, you need to keep throttle up to have maximum lift -- this makes landing a challenge.  In fact, it is a great reason to have air brakes of some sort.
Anything that affects just parasite drag -- without changing the lifting capability of the wing -- will not change stall speed.  So, landing gear, speed brakes, stores on the wings, an open door or window, installing an antenna or sensor, etc.

So, you are saying if I deploy the spoilers, that won't affect my stall speed either?

Spoilers obviously do cause changes to stall speed -- that's the whole point -- but not due to parasite drag. It's because you're breaking up the streamline flow over the wing. What a strange gotcha...

As @DarthPseudonym said, spoilers will effect stall speed -- but spoilers are a device designed to spoil lift and to create drag.  You would never use spoilers on takeoff.  You would use them on landing -- perhaps even only after wheels down.

ok you got me, then what about if the spoilers aren't "spoilers", but air brakes in the back of the plane like the BAe 146 ? isn't this parasite drag and doesn't it affect the stall speed?

Great example.  Lots of parasite drag.  No effect on stall speed.

ok I guess now you also got me.

Ok I got my confusion clear. I was confusing that because of the drag i was going to stall sooner which meant that my stall speed increased, but in reality my stall speed stays the same all the time, its just that I will get sooner to my stall speed the more drag I add to the airplane because I'm reducing my speed quicker.


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Above which altitude an airplane is required to have oxygen mask for the passenger?
Is there a maximum altitude above which an aircraft needs to have oxygen mask available for the passengers?

14 CFR 91.211 spells out the supplemental oxygen requirements:

(a) General. No person may operate a civil aircraft of U.S. registry
(3) At cabin pressure altitudes above 15,000 feet (MSL) unless each occupant of the aircraft is provided with supplemental oxygen.

For Pressurized aircraft:

(i) At flight altitudes above flight level 250 unless at least a 10-minute supply of supplemental oxygen, in addition to any oxygen required to satisfy paragraph (a) of this section, is available for each occupant of the aircraft for use in the event that a descent is necessitated by loss of cabin pressurization; and...

Note that it doesn't specify a "mask", (some GA systems use a delivery system to the nostrils) or that the passengers are required to use what is provided or available.

Does this means that a pressurized aircraft certified to fly max altitude FL 24 doesn't need to have the typical passenger supplemental oxygen masks that drops when the aircraft losses pressurization?

Apparently that is correct.

perfect that was my doubt. thanks

@Gabe It's up to FL250. Planes without masks with FL250 ceilings include the Dash 8 (optional masks extend to FL270) and ATR-42/72 (there's only masks for 25% of the passengers, cabin crew manually release them for passengers that need it).


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Is there any electric aircraft certified by the FAA?
I see this EASA publication about the Pipistrel Velis Electro being certified on 2020(almost 4 years now). Is there any electric aircraft certified by the FAA? and if not is there any reason why not after EASA already certified 4 years ago or is just no manufacturer has applied for electric aircraft certification with the FAA?
P.S.: Can the Pipistrel Velis Electro currently fly in the USA?

Is there any electric aircraft certified by the FAA? It depends on your definition of "aircraft." The FAA has certified several unmanned electric aircraft such as the Matternet M2, Aerovironment PUMA AE, and Airobotics OPTIMUS 1-EX. However, no manned electric aircraft has been certified at this time.
It's not for lack of interest from manufacturers. There are many companies working towards certifying electric aircraft. Pipistrel has applied for FAA approval and is working towards a certification. The issue is that this is a new type of aircraft (or at least propulsion) and the FAA works slowly. In addition to the usual concerns of certification, the FAA would probably like to avoid any high-profile issues, as recent history has shown how quickly people can lose trust, especially with a new technology like electric aircraft.
Can the Pipistrel Velis Electro currently fly in the USA? It depends on your definition of "fly." It's already flying in the US under experimental rules. It would need FAA certification to fly commercially though. The US Air Force will also be experimenting with it, which also doesn't necessarily require FAA certification.
The FAA has been working towards rule changes for smaller aircraft that would make it easier to certify them, including these kinds of electric aircraft. Another type of electric aircraft with lots of interest is eVTOL (electric Vertical Take Off and Landing) and the FAA is looking at creating a new category to certify those.
And it's not just the FAA that's moving slowly. The Velis Electro is apparently still the only electric aircraft with EASA certification. A lot has been going on in the world in the last 4 years and continues to occur. Yet still technology moves much faster than regulations and as both continue to advance there will likely be more electric aircraft being certified. Not as soon as many would like, but with time the industry will grow.

Great, could you answer this related question: https://aviation.stackexchange.com/questions/105714/can-you-fly-a-newly-easa-type-certified-aircraft-in-the-usa

It seems the eFlyer 2 is working on FAA certification. This article from a year ago seems to imply that it is on track to be the first.
Per 14 CFR § 21.190, it should be possible to register one in the US in the LSA category since the US has a bilateral agreement with the EU.

I’ve seen those guys from by aerospace, and to be honest with you, they’re more courting investors that really trying to achieve anything.  They have been claiming that airplane will be certified next year for the past five years.  they’re stuck in a situation where their bets on battery technology did not live up to actual progress, and as a result, they have an airplane with hamstrung capabilities and nowhere to take the investment.


text:
Is there a relationship between ocean tide and turbulence?
Especially at lower altitudes, can we asume that if the tide looks high that there would be more turbulence and vice versa?

Why would you think that?

because I've noticed it is windy when the tide is high and I wondered if that translated  to turbulence on the air just like choppy waters at sea level.

Well, high (onshore) winds can sometimes cause slightly-higher tides but it's normally a rather small effect compared to the normal range of the tides -- I really doubt that there's a robust correlation between tide height and wind speed generally --

No.
In places such as the English Channel where tides cause strong tidal currents,
these can increase wind by as much as 1.5 m/s, or 3.5 mph
(Fig. 4 of Renault & Marchesiello,
"Ocean tides can drag the atmosphere and cause tidal winds over broad continental shelves,"
Nature Comm. Earth & Env. 3: 70 (2022).
But this is only within 800 m of the ocean surface,
and only where tides cause currents.
Also, a wind speed increase of 3.5 mph, from 0 to 3.5 or from 20 to 23.5,
is too small to increase turbulence enough to notice from even a small lightweight airplane.
High or low tide by itself, say
in the mid-Atlantic or mid-Canada (which moves up and
down too, "crustal tide"),
is too small in amplitude, and changes too slowly, to affect wind speed
nevermind the amount of turbulence.
Although tides are felt by not just sea and land but also the air,
these lunar atmospheric tides
affect wind even less.

Agreed, on the other hand, wind and low pressures affect sea level and tidal range in relation with the local geography (English Channel, Adriatic Sea, ..., 2m increase in the Baltic Sea). This is investigated, e.g. to improve tidal barrier operations: Thames barrier and Venice barrier.

Sure, atmospheric phenomena ("weather") can affect local water level.  But the question sounds like it wants to infer how much turbulence there is, which you could do by observing the weather itself instead of something that it affects.


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Why did Boeing shrink the bottom of the engine casing instead of the whole casing?
It is known the reason of the distinguishing flattened engine casing on the 737 was to increase the ground clearance after they upgraded to a bigger engine.

(source)
However, why didn't Boeing just shrink the whole casing instead, thus giving a perfect round casing?
Or is there an advantage of having a flattened bottom casing in general other than ground clearance? lifting body effect?
Are thin or thick casings better than the other?

Because they wanted a large inlet area?

Related: Why are the Boeing 737 nacelles odd shaped?

Not only was it flattened, it still needed to move forward on the MAX because it needed to sit a little higher, which altered the flight characteristics of the new plane, making it unstable, which is why they introduced software which would override the pilot when the new, tighter flight envelope was exceeded, but that could not go into the manual because that would have made new pilot certifications necessary, which is why the pilots didn't know about it when it malfunctioned.

@Peter-ReinstateMonica - the MAX engine location did not make the plane unstable, instead in specific high AOA and no flaps situations it caused the nose to pitch up in reaction to pilot input more than previous 737s.  While not unsafe by itself, the concern was that a pilot not trained for this different handling characteristic could inadvertently give too much yoke input which could be dangerous. To avoid expensive simulator training requirements for their customers, Boeing implemented MCAS to essentially dampen the pilot's input in these situations so that it flew like previous 737s.

@StevePemberton I think it is acceptable to describe "previously tolerable input leads to dangerous situations" as "unstable". Maybe not unstable in the sense of a helicopter but less benign.

Usually the accessory gearbox (AGB) of the engine is located at the bottom of the engine. This gearbox spins different accessories, of which the electrical generator, and hosts the starter which drives the high pressure shaft (N2) of the engine:

Usual bottom position of the AGB, here on a CFM56-5B used for A320. Source.
When CFMI had to design the CFM56-7B engine for the Boeing 737 NG, with wings closer than usual to the ground, the AGB was moved to the side of the engine:

Unusual side position of the AGB on a CFM56-7B used for 737 NG. Source.
With the AGB on the side of the fan case, the nacelle can have a flatter bottom, allowing to reach the required ground clearance, but its horizontal "diameter" is larger. Compare versions 5B of the CFM56 (A320) and the flattened 7B (737 NG):

Source. In addition, the fan of a 5B has a diameter of 68", the fan of a 7B a diameter of 61", much smaller.
See also Where is the generator in a large turbofan of a commercial airliner?.

I don't think the AGB is the main reason because many large and small engines mount it on the core. That's exactly what they did on the PW1000G. Other examples include CF34 (except -10 series), PW4000, JT9D, GE90.

@user71659: The CFM56 core was modified from a U.S. military design; maybe the restrictions placed on the engine core as a condition of allowing its export made putting the CFM56's gearbox on its core impossible?

@mins Not obvious, your diagram shows plenty of yellow space. And look at the CF34-8, it's way in there.

@mins Why is it still on the bottom? The E190/CF34-10 AGB is at 3 o'clock and the bulge/flattening is far less obvious. I maintain cowling aero is the primary design driver, the fact that they still could fit the AGB in its profile is secondary. If they couldn't, they'd have gone to core mounting.

@mins And again, look at the CF34-8. It's still accommodated with a narrowing of the fan duct.

@user71659 Presumably putting the AGB with all of the stuff on it on the core creates an obstruction to the bypass airflow, reducing thrust and efficiency. So it will be a trade-off between that and making the nacelle wider (and thus draggier).

@TooTea To minimize nacelle area, you end up with the design of the A320neo LEAP with the bulge on one side only.

@mins: Another point that favors the reasoning in your answer: rotating the location of the components is way less extreme than the complete re-engineering of the systems-integration, and this also maintains the accessibility for the line maintenance (topping off the oil, etc.).

why didn't Boeing just shrink the whole casing instead, thus giving a perfect round casing?

Short preface: The so-called capture area of the engine's inlet, i.e. the area as seen from the front, is chosen to supply the engine with the needed airflow mass at all flying conditions. The airflow mass is a known number from the engine manufacturer and the capture area is simply proportional to it.
Short amendment to your question: when Boeing updated the old low-bypass P&W JT8D with the newer high-bypass CFM56, the casing was actually stretched, not shrunk.
The newer CFM56 needed some 300kg of air per second instead of the 210kg/s of the older JT8D: this translated into a capture area 300/210=1.43 times bigger i.e. into a 20% bigger diameter. The problem faced by Boeing's engineers was therefore not of how much the inlet should have been shrunk to keep it circular, rather how to ensure that the now bigger inlet didn't scrape against the tarmac! The problem was solved with what is now considered the very first remarkable industrial application of the, back then emerging, CFD: the nacelle was placed very close to the wing without altering too much the spanwise lift distribution on the wing, which is responsible for the induced drag. Before that, the inlet was empirically placed always one diameter under the wing and two diameters in front of it: any other placement was found to increase drag. To further increase ground and FOD clearance, the bottom part of the inlet was flattened and the engine accessories were relocated from the bottom (where they are usually located) to the side as well. All these tricks have given the B737's nacelles their iconic shape.

Is CFD "Computational Fluid Dynamics"? Might be worth spelling it out. I'd edit the answer.... But I might be wrong. :-D

@GrimmTheOpiner: I linked the relevant Wikipedia entry, thanks for the suggestion

Complementing @mins' answer and analysis:
Boeing's engineers wrote about it in an engineering journal in 1982, so this is from the horse's mouth:

The nacelle had several design constraints which necessitated an innovative design approach to attain the proper shape and contour lines. Ground clearance considerations required the engine manufacturer to place the gearbox and accessories on the sides of the engine or cheeks of the nacelle (Fig 19), with the drive removed from the bottom centerline. This tended to flatten the bottom of the nacelle and influenced the shape of the inlet lip to a near circular upper half and a near elliptical lower half. A large radius lower lip leading edge was provided which was shown by wind tunnel tests to have excellent pressure recovery.
Source: Baer, Jerome C., and Allan L. Schuehle. Re-engining the 737. No. 821442. SAE Technical Paper, 1982. https://doi.org/10.4271/821442

In summary: the relocating of the accessories (a simple band-aid rotation in effect) is due to the ground clearance of an existing engine; that is what resulted in the "near elliptical lower half" and the larger radius lower lip. Comparisons with the CF34 are both a faulty generalization and false equivalence, as engineering is a compromise and the CFM56 wasn't built from scratch for the 737, respectively.
And here's the aforementioned figure:

Highlighting mine

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text:
Horizontal oval windows in Cessna aircraft
Is there a reason (except aesthetics) behind the horizontal oval form of the windows of some private jet/small aircraft?
As far as I'm aware this shape should be rather counterproductive. According to the following diagram, a lying oval is the worst stress-wise and a vertical oval (similar to commercial aircraft) would be better:
Y-axis depicts stress-factor

A higher stress-factor results in higher structural weight.
The diagram assumes monoaxial stress. I think the stress in the tangential direction of the hull should be much greater than the stress in the longitudinal direction.
E. g. a Cessna 300 Series aircraft:

Y'know what would be even safer? NO windows at all!

In a fuselage that small, a tall window might have to go through a longeron, or be so small as to be not worth the trouble.

Can please show a reference for the image?
Keep in mind that your diagram is only valid for stresses in the horizontal plane. In case of vertical stresses, you flip the image 90 degrees, and the horizontal windows are suddenly the best.

"A higher stress-factor results in higher structural weight."
Yes, because you have to put enough material to resist the stress arising from the high stress factor.

"I think the stress in the tangential direction of the hull should be much greater than the stress in the longitudinal direction" it strongly depends on the fuselage shape, so saying anything in general is difficult.

Is it a Cessna 300 or 400?

You are reading the graph the opposite way you should read it. In the extreme case of a "horizontal flat" windows (i.e. a window with zero thickness, i.e. no windows as funnily but correctly suggested by @A.I.Breveleri), the stress concentration factor (/y-axis) is 1, i.e. the maximum stress is the same as the far field stress acting on the intact fuselage.
For an elipsoid elongated in direction of the maximum tensile stress, the stress factor is always smaller than the stress concentration factor of a rounded or eliptical-in-the-other-direction windows (exactly the line you point in the graph is always lower than thew other two).
The reason maybe is that for small plane the maximum stress is due to the fuselage itself carring the tail/nose load (therefore horizontal), while for big planes it may be due to pressurization (therefore radial i.e. "vertical")?
The stress direction is probably changing along the fuselage. too, and it may even change due to dynamic conditions during the life of the plane.
If you look carefully at the Cessna 400 windows, you will see that the shape is slowly changing with distance from the wings (see photo here), probably to minimize the fuselage material required to support stress factor from varying loads, as well as to optimize for the stresses (towards the tail they may come from all directions, so a rounded shape is a one-size-fits-all, while close to the wings the stress are more close to horizontal, so one can save fuselage material and weight by having horizontal elipsoid).
In short: these windows are extremely ugly, no aesthetics whatsoever can be possibly involved, it is just engineering to provide the maximum windows area possible without needing to add two engines to fly the resulting reinforced brick.

Regarding the windows getting smaller towards the end, isn't that just a consequence of the fuselage tapering and thus the 'roof' coming down? If you would keep the same size windows, you would run into the tail ventral fin

Humans are naturally more interested than scanning left and right along the horizon than scanning up and down.
We inherently tend to disregard or mentally minimize objects that are located far from the horizon.  That's why the full moon looks huge when it is just above the horizon, and tiny when it is high in the sky.
The window designers designed the windows to give the humans the largest view of the part of the visual field that the humans were most interested in.
By shaping the windows to prioritize the part of the visual field that inherently seems "biggest", the illusion is created of a greater overall field of view.
Also, by avoiding tall windows, the sun is less likely to shine into the passenger's eyes.

These reasons also apply to airliner windows, but those are tall not wide, so something structural not just physiological must be guiding such decisions.

Just about the only windows where visibility is the key requirement are the ones up front. Aside from very specific cases, the rest are more about aesthetics and efficiency.


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How does tip stall severity vary between normal tapered, leading-edge tapered, and trailing-edge tapered wings with the same taper ratio?
I'm trying to understand how the geometry of a wing's taper affects tip stall severity. Assuming the taper ratio is the same, how would the tip stall characteristics differ between:

A wing with a standard (symmetric) taper.
A wing with leading-edge taper only.
A wing with trailing-edge taper only.

Does the location of the taper (leading vs. trailing edge) influence the stall behavior significantly? If so, what are the aerodynamic reasons behind this difference?
I have gone through aircraft design textbooks by Raymer , Saadrey and snorri but couldnt find a proper answer.

Some elements in Why do tapered wings not stall at the root first? (also comments).

This might also help.

I read your question as shown in the sketch below. The expressions  leading-edge / trailing-edge taper are not clearly defined. I hope I understood you correctly.

With an aspect ratio of 6 or greater, the small amount of sweep introduced by tapering will be insignificant for stall. It is much more important to pick a tip airfoil with benign stall characteristics and add washout so the wing will stall at the root first. With more taper, more washout will be needed.
For smaller aspect ratios you will see progressively worse stall behavior in leading-edge tapered wings the smaller the aspect ratio becomes because they will behave similar to a sweptback wing. Since the trailing edge is still straight, this will never be as severe as in a "real" swept-back wing and can be easily cured with washout. A trailing-edge tapered wing, therefore, will require a bit less washout than a leading-edge tapered wing.
For very small aspect ratios the leading-edge tapered wing will behave like a delta wing, so boundary layer effects will become less important than the effects of vortex lift.

Here are some lift and lift coefficient distributions for wings that fit your description.
The span is 10.  The root chord is 1.0.  The tip chord is 0.4.
No twist, symmetrical airfoils, 5 deg alpha.
These were calculated using VSPAERO in thin-surface (VLM) mode.
Straight LE:

Straight C/4:

Straight TE:

As you can see, for this case, sweeping the wing aft shifts the lift coefficient distribution slightly outboard and increases the peak lift coefficient slightly.  This will move stall outboard some and possibly reduce the angle of attack of stall.
However, both effects are very small in this case.
There are a tremendous number of interacting variables in problems like this -- this makes it very hard to establish a set of simple rules that always hold (why you don't see details like this in textbooks).  Instead, it is very easy to do some computational experiments using tools like VSPAERO, AVL, XFLR5, Tornado, or others -- or to write your own VLM code and try that.